In order to improvement electronic and mechanical properties, welding between stranded wires and terminals is important. However, welding methods to obtain high-quality joints using stranded wires ...are still limited. In this report, we applied ultrasonic welding to join a Cu stranded wire to a Cu substrate. Cross-sections of the weldments were taken and observed by several microscopy techniques to elucidate the weldability and soundness of the joints. After ultrasonic welding, each wire in the stranded wire was joined together at the region where the stranded wire was joined to the substrate without any defect. Each wire was welded through the Ag coating layer, and the stranded wire and the substrate was also welded through the outermost coating layers. It was found that ultrasonic welding is an efficient technique for producing high quality joints without any defect at the interface.
The welding of hygroscopic materials such as polyamide can lead to unstable conditions during the welding process. Due to changing material properties, the ultrasonic welding process is influenced ...heavily by the moisture level of the welding parts. To achieve stable welding processes and high weldline qualities, it is necessary to understand the influence of moisture on the material properties and the ultrasonic welding process. To perform a scientific examination of the influence of moisture on the ultrasonic welding process, the interactions between the material properties and the welding process are determined in relation to the moisture content. With the aid of welding tests, it can be shown that with constant welding parameters, the attainable weld strength decreases with increasing moisture load. Microscopy analyses show gas bubbles in the weld seam. These are formed during the welding process, because of the evaporation of water in the welding zone. Furthermore, it can be seen that the time required to reach a predetermined welding path depends on the moisture content. At first, the welding time increases with increasing moisture content and is decreasing again with further moisture load. In order to explain the welding behaviour, material tests are carried out. Especially, the material damping influences the welding process largely in case of ultrasonic welding. The material damping in dependency of temperature and frequency can be described by storage and loss modulus. To determine loss and storage modulus at the welding frequency of 20 kHz, dynamic mechanical analyses are carried out at different temperatures and frequencies. The results are extrapolated by making use of time/temperature shift to 20 kHz. The results show that at 20 kHz, the maximum material damping is not exceeded in case of the maximum moisture load but at the same moisture load as in case of the maximum welding times. Further welding tests show that the welding time can be decreased again by choosing a higher welding amplitude, which leads to a higher energy input in the specimens. However, the weld seam strength cannot be increased to the stage of the dry-welded specimens by adapting the welding parameters, because of the formation of gas bubbles in the weld seam strength.
This paper presents a novel straightforward method for ultrasonic welding of thermoplastic-composite coupons in optimum processing conditions. The ultrasonic welding process described in this paper ...is based on three main pillars. Firstly, flat energy directors are used for preferential heat generation at the joining interface during the welding process. A flat energy director is a neat thermoplastic resin film that is placed between the parts to be joined prior to the welding process and heats up preferentially owing to its lower compressive stiffness relative to the composite substrates. Consequently, flat energy directors provide a simple solution that does not require molding of resin protrusions on the surfaces of the composite substrates, as opposed to ultrasonic welding of unreinforced plastics. Secondly, the process data provided by the ultrasonic welder is used to rapidly define the optimum welding parameters for any thermoplastic composite material combination. Thirdly, displacement control is used in the welding process to ensure consistent quality of the welded joints. According to this method, thermoplastic-composite flat coupons are individually welded in a single lap configuration. Mechanical testing of the welded coupons allows determining the apparent lap shear strength of the joints, which is one of the properties most commonly used to quantify the strength of thermoplastic composite welded joints.
Lithium-ion battery cells of pouch type for battery electric vehicles are often joined by ultrasonic welding. High-frequency vibration generated by the piezoelectric transducer of the welder creates ...solid-state bonds between the workpieces via interfacial frictional heat. This vibration, however, can cause parasitic vibration of the entire system that is harmful to the structure (such as destroying existing welds). In this study, a modulation of input waveforms of the ultrasonic welder is proposed to reduce such parasitic vibration. A series of vibration models are analyzed: (a) a discrete model of single-degree-of-freedom (SDOF) mass–spring–damper system to understand rigid body dynamics, (b) a continuous model of multi-degree-of-freedom (MDOF) cantilever beam to study an elastic body system, and (c) a battery welding system to study a complex real-world application. Analyses indicate that the waveform modulation (including 180°-phase shift, pause, amplitude stepping, and frequency modulation) can reduce parasitic vibration while improving or maintaining the quality of the weld that is being ultrasonically made.
The present study was conducted to investigate how the characteristics of welds are affected by the horn-tip pattern shape, in order to assess how to efficiently transfer the vibration energy to a ...base material through the horn. Energy transfer was evaluated using the indentation marks. The experiment was carried out with aluminum and copper by combining the conditions from four horn-tip patterns, six pressure values, and ten welding time values. The aspect ratio of the indentation marks on the weld surfaces was measured. The effects of the applied pressure, welding time, and horn-tip pattern shape on the aspect ratio were analyzed, and it was found that the horn-tip pattern shape affects the aspect ratio significantly. The aspect ratio was suggested as an analytical reference, and its correlations with the shear strength and the hardness of the welds were verified. In addition, the experiment performed with aluminum and copper, which have different mechanical properties, under the same welding conditions showed that the aspect ratio was dependent on the mechanical properties of the materials. In conclusion, as the density of the horn-tip pattern is decreased, less of the vibration energy was lost, increasing the strength of the welds. Experimental results showed that shear strength of copper was nearly 400 N when the aspect ratio was close to the value of 1. The highest peak of horn-tip pattern forms the lowest aspect ratio of the indentation mark, which can be indicated that the decrease of the aspect ratio effect to the improvement of welds strength. Aspect ratio of horn-tip pattern D, which dimensions are pitch 1.5 mm, height 0.75 mm and stub tooth 0.7 mm was closely to the value of 1 compared to the other patterns.
This review work is to summarise the results of the experimental studies on ultrasonic welding of thermoplastics, blends of thermoplastic polymers and composites at Department of Engineering ...Technology, Technical University of Liberec, Czech Republic. The previous studies were focused on determining the effect of selected technological parameters in ultrasonic welding process, of different energy director shapes and of filler percentages in the thermoplastic matrix on the tensile strength of the welded joint under various welding conditions. In addition, this review also mentions the further research directions in this field.
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